Inorganic and Organic Surface Passivation Effects on the Structural and Electronic Properties of Silicon Quantum Dots: Ab-initio Study

A series of an ab-initio calculation has been done to study the change of structural and electronic properties of silicon quantum dot caused by inorganic compound, hydroxyl (OH) and organic compound, methyl (CH3)passiviants. Geometrical optimization shows that the fully saturated passivated structures were possible, after undergone surface reconstruction without any dangling bond left. We also found that there were a bond increment for the silicon-hydroxyl bond at structural surface. Meanwhile, distortion were also noticed during dynamical relaxation process at the quantum dots core region. For methyl passivation compound, there were significant increments of bond length for the silicon-methyl bond, while the symmetrical of tetrahedral geometry were preserved at core region. This will contribute to the clear confinement effect on methyl passivated quantum dots. Shortly, both passiviants effect on electronic properties of the silicon quantum dots can be simplified in three perspectives. First, there were significant reduction of the energy-gap when the passiviants used were highly dynamical movement that caused a distortion on the core structure. Second, both passiviants does influenced the energy-gap of quantum dots, however the direct gap behaviour of this nanocrystal still preserved. Third, the presence of mini-gaps energy gap were quite noticeable for small clusters, unfortunately it can reduce the quantum yield of exitonic process.